Rengoku Kyojuro and Himejima Gyomei also arrived on the scene.
They saw that Kokushibo still possessed the strength to fight—and they saw Nightingale, standing there holding Kibutsuji Muzan's severed head.
Why hadn't Nightingale simply destroyed Muzan? Was she worried about causing the Infinity Castle to collapse?
They could all guess why Muzan was behaving so quietly now. The poison in his body had crippled his regenerative abilities—at this moment, Muzan must be focusing everything he had on breaking down the toxins inside him.
He had already consumed the Blue Spider Lily. If he could fully neutralize the poison, Muzan would truly become immortal.
At that moment, Nightingale suddenly looked up, eyes meeting Rengoku Kyojuro's as he stood atop a shattered platform.
"Rengoku-san, may I borrow your sword for a moment?"
Rengoku blinked in surprise, not understanding why Nightingale would suddenly ask for his blade.
If it was for slaying demons, Nightingale already possessed weapons far more effective than a Nichirin Blade.
"Of course! I have no objection!"
But out of trust for Nightingale, Kyojuro sheathed his sword and tossed it—scabbard and all—down to her.
Still gripping the subdued Muzan in her left hand, Nightingale caught the blade with her right.
With her left arm occupied, Nightingale tucked the scabbard under her arm and drew the Nichirin Blade with a practiced motion.
Nichirin Blades, also called "Color-Changing Swords," took on hues unique to their wielders—Tanjiro's turned jet black when he first held it; Zenitsu's was golden-yellow.
Rengoku's blade was a vivid crimson, engraved with flame motifs, its tsuba shaped like a burst of fire.
Seeing this blade, Nightingale recalled the original story—how Kyojuro fell during the Mugen Train battle, and this flame-shaped tsuba was entrusted to Kamado Tanjiro, who hoped it might adorn a new sword. Later, it was with this new blade that Tanjiro and the others finally defeated Muzan.
She also remembered that, during Gyokko's attack on the Swordsmith Village, a young boy named Kotetsu survived only because the flame-shaped tsuba he wore blocked a lethal blow.
If I'm going to do this… perhaps this sword is the most fitting after all…
Nightingale relaxed her arm, letting the tip of the blade dip toward the ground.
It was an astonishing sight.
On a battlefield ravaged and torn, the very hands that had saved countless lives now gripped a weapon meant only to kill.
No one had ever imagined they'd witness such a scene.
"Nurse-san… can she use sword techniques too?"
Uzui Tengen couldn't help but ask, naturally turning to Shinobu—the person who knew Nightingale best.
"Um… I think so?" Shinobu replied, uncertainty in her voice.
"How are you not sure?" Tengen retorted.
In truth, Shinobu had never actually seen Nightingale wield a sword—only that she could perform a strange movement technique called [Shukuchi].
None of them could understand what Nightingale was about to do. But facing her now, Kokushibo felt something very different.
The moment that woman gripped the sword and turned her red eyes on him, all the "presence" and "qi" of the world seemed drawn uncontrollably to her.
It was as if a mountain had been set across his shoulders—the air itself turned heavy with pressure.
Though her posture looked casual, almost thoughtless, Kokushibo couldn't discern a single opening.
Yes… yes… yes…
Just like four hundred years ago. Just like that man…
Four centuries past, a man who seemed blessed by all the gods was born into this world.
Because he was born with a flame-shaped Mark, his father thought he would bring disaster and tried to kill him—only his mother's desperate intervention saved him.
Spared that fate, the boy was destined to be sent to a temple at age ten.
His name was Tsugikuni Yoriichi—the younger brother of Kokushibo… or rather, Tsugikuni Michikatsu.
From childhood, Michikatsu grew up under the weight of everyone's expectations, striving to be the next Tsugikuni head, never daring to relax.
Yoriichi was shut away in a small room, forbidden from being approached by the rest of the family.
Michikatsu always pitied Yoriichi—he'd never smiled since birth, never spoken a word until he was seven, always clinging to their mother like a child seeking comfort.
Until that day—
Michikatsu's own sword master, whom he'd struggled so long to even hope to match, was defeated by Yoriichi the very first time he picked up a blade.
Something Michikatsu had worked for all his life, Yoriichi achieved without effort.
Yet after that, Yoriichi never touched a sword again—he disliked the feeling of cutting into flesh.
Their father eventually discovered Yoriichi's talent, and the brothers' fates were swapped: Yoriichi would inherit the family, while Michikatsu would be sent to the temple.
His dream was to become the world's greatest samurai—but now that dream was shattered, all because of the brother he had pitied.
But one day, Yoriichi quietly left the family.
Michikatsu became the clan head after all, fulfilling his wish in the most unexpected way.
He gained status, a happy family, loyal retainers.
If nothing had happened, perhaps he could have lived a simple, peaceful life.
But then, a single demon slaughtered all his retainers.
And then Yoriichi reappeared.
With swordsmanship honed to perfection, he slew that demon in a single stroke—leaving Michikatsu reeling in utter defeat.
To pursue that power, Michikatsu abandoned his family, his clan, everything he'd ever worked for, becoming a Demon Slayer like Yoriichi.
Yoriichi shared his techniques with everyone, but no one could master them—so he taught each person a breathing style suited to them, and soon, many Demon Slayers awakened their Marks.
Michikatsu, too, bore a Mark—one nearly identical to Yoriichi's—but he could never learn Yoriichi's Sun Breathing. What he had was merely a derivative, which he named Moon Breathing.
If I trained even harder… could I one day catch up to Yoriichi? But as he struggled with this resentment, he learned the truth: marked swordsmen never lived past twenty-five. He had no future at all.
But Kibutsuji Muzan's arrival gave him a new path. Once again, he abandoned everything, became a demon, gained eternal life—and for centuries, refined his techniques, finally believing he'd surpassed Yoriichi.
And then, under a blood-red moon four hundred years ago, he met the brother he'd thought long dead.
Yoriichi was eighty by then—white-haired, shriveled with age.
And yet, Michikatsu lost again.
Speed, power—there was not a hint of decline from Yoriichi's prime. Michikatsu saw no hope of victory.
Why are you always so extraordinary?
Why do you always make me feel so wretched?
One more cut and he'd have been finished. Any resistance would have been meaningless.
But in the end, he survived.
That man—that godlike swordsman—died standing, simply because his lifespan ran out.
Humiliation… ridiculous!
Yoriichi… how long will you continue to mock me?
You forced me to see you as someone beyond all reason, only to die of old age, never giving me a single chance to win!
Yes, Yoriichi was dead. Michikatsu had watched his life fade away with his own eyes, had personally cut the corpse in half.
And yet now, as Nightingale stood before him, sword in hand, her silhouette overlapped with the man he most hated.
So much hate… so much hate!
Kill! Kill! Kill!
"Die—!!"
Blades born of his own flesh—dozens, hundreds—swung at once in a wild, vengeful dance.
[Moon Breathing, Fourteenth Form: Catastrophe, Tenman Crescent Moon]
A sudden storm of sword energy erupted, swallowing the battlefield in chaos. There was nowhere to hide—everything in the range of that attack was obliterated.
Even though Nightingale still held Muzan, even though Muzan had lost his regenerative power, Kokushibo didn't hesitate. He had lost all reason, all he wanted was to kill Nightingale—or rather, kill the nightmare that had haunted him his whole life.
Maybe it was true desperation. The power and range of this attack were staggering. Even from a distance, the Hashira were left trembling by the quake and shockwave.
"Damn… How can he still have this kind of strength?"
"He's already lost all human form… that monster…"
"Sensei!!"
They felt as powerless as blades of grass in a hurricane.
Forget approaching—they couldn't even stay on their feet. Anyone who didn't huddle to the ground and cover their heads risked being swept away by flying debris or the storm itself.
"Die! Die! Die! Why won't you die?!"
Twisted beyond recognition, his organs corroded by poison.
Blades snapped and regrew.
Flesh rotted away and was replaced.
Every moment, agony tore through his entire being, down to every last cell.
But… but!
Compared to this humiliation, compared to five centuries of torment—pain was nothing.
Swing, swing, swing.
He poured every scrap of mastery forged over five hundred years into his sword.
But… it still wasn't enough—not nearly enough.
The opponent was Yoriichi—a being untouched by all, even Muzan himself.
Being "perfect" wasn't enough. He needed to go further. He had to try harder.
Surpass perfection. Surpass even himself!
Every swing, stronger than the last! Faster than the last!
"Die! Die! Die!"
Teeth shattered in his mouth, but the raging storm soon drowned out even that sound.
I know. I know everything. I'm nothing but a painfully ordinary man, while you… you're heaven's chosen genius.
Centuries of sacrifice and training… but my success isn't because of these. It's only because a true genius never cared for them—so they fell to me instead.
Your effortless freedom makes all my struggles seem like a joke.
Why does the world allow someone as unreasonable as you to exist?
I'll burn myself out—I'll give everything I have.
I'll risk it all! I can't bear another defeat!
One lifetime of humiliation is enough!
Come! Five centuries of hatred, burning until all reason evaporates!
Come! Five centuries of rage, scorching my insides!
Even if only for a moment—let this moonlight eclipse the sun!
Even if only once—let me win!
"—YORIICHI!!"
A scream, raw and hysterical.
In that moment, Kokushibo truly surpassed himself.
Even if Gyomei and the others could return to the peak of their power, they could never hold their own against this strike. They would be cut down before they realized what happened; the battle would end in an instant.
Kokushibo threw everything onto the fire, pushing his skills to heights never reached before.
And then, in the very next instant… Kokushibo saw a flash of fire.
No, not fire—a blazing sun.
The searing sunlight took shape, and in a heartbeat, tore through Kokushibo's body.
His body grew impossibly heavy. His consciousness was being pulled down, as if by some unseen force.
In that single instant, Kokushibo understood… this was death.
In his final moments, the last thing Kokushibo saw… was a broken wooden flute.
I will treat this flute you gave me, Brother, as if it were you.
No more…
I hate you so much…
Just seeing your face makes me want to vomit, hearing your voice fills me with fury, my head splitting with rage.
I abandoned my family, my wife and children, my humanity itself. In the end, I even gave up my life and everything I'd built over centuries.
Even after all that—it still wasn't enough?
You once said, "Those who pursue the way, in the end, all reach the same place." But I can never reach where you are—I can't see the world you saw.
Even after your death, even after Muzan and I wiped out all who knew Sun Breathing… why does your breathing still remain in this world?
Why can't I leave anything behind? Why can't I become anyone? Why am I so different from you?
Why was I born into this world? Tell me… Yoriichi…